Fuel systems including fuel tanks may be used to store and provide fuel to engines. For example, a vehicle including an internal combustion engine may include a fuel tank that stores liquid fuels such as gasoline, diesel, methanol, ethanol, and/or other fuels.
Liquid fuels in a fuel tank may evaporate into fuel vapors in the tank. As such, various fuel vapor management systems may be included in a fuel system. Such fuel systems may be substantially sealed from the atmosphere but may include components configured to vent the fuel system to the atmosphere during certain conditions. For example, a fuel system may include a vapor purge canister for filtering fuel vapors during venting.
If there are leaks in the fuel system, e.g., if there are leaks in the fuel tank, canister or any other component of the vapor handling system, then fuel vapor may escape to the atmosphere contributing to vehicle emissions, for example. Various approaches to diagnosing leaks in vehicle fuel systems are known. In one approach, leak testing is achieved by utilizing a vehicle engine to create a vacuum within the fuel tank and measuring pressure changes over a time period.
In one example approach, an external vacuum pump may be used to create a vacuum to perform a leak test in a hybrid vehicle system. However, the inventors herein have recognized that such an approach may increase material and installation costs associated with the installation of such an external vacuum pump and associated hardware and software.
As another example approach, an engine in a hybrid vehicle system may be run specifically for performing leaks tests during engine-off operating modes, for example. However, the inventors herein have recognized that running the engine to perform leak tests when the engine is not used to propel the vehicle may result in a decrease in gas mileage since, in this example, fuel is consumed while performing the leak test.
In some approaches, engine off natural vacuum (EONV) may be employed for leak testing in a hybrid vehicle system. For example, a normally closed canister vent may be opened and a decrease in vacuum may be measured over a long period of time. Such approaches may use correlations between temperature and vacuum build. However, the inventors herein have recognized a number of issues with such EONV approaches. For example, additional hardware and software may increase costs, and long test times in may reduce the feasibility of carrying out a leak test. Additionally, such EONV approaches may degrade during hot ambient temperature conditions. Further, such EONV approaches may not be sufficiently accurate for leak testing, e.g., due to unreliable correlations between temperature and vacuum build (e.g., due to mass transfer between the liquid and vapor in a fuel tank).
The inventors herein have recognized the above deficiencies, and addressed them, in one example approach, by a method of operating an engine emission control system including a fuel vapor retaining device coupled to a fuel tank through a valve is provided. The method comprises: during an engine off condition, selectively operating a fuel pump to store at least some pressure in an accumulator coupled to the fuel pump; and using the stored pressure to determine a leak in the emission control system. In some examples, selectively operating the fuel pump may include operating the pump until a pressure in the accumulator reaches a threshold, and then discontinuing operation of the fuel pump. In other examples, selectively operating the pump may include operating the pump for a selected duration, where the duration selected is based on accumulator pressure.
In this way, the amount of new hardware and/or software used for leak testing may be reduced, resulting in lower material and installation costs, since the fuel pump can be used for engine-off leak detection, as well as engine running fuel supply to the combustion chambers of the engine. Thus, the same pump may be used for leak testing and for supplying fuel to the engine, resulting in a reduced amount of hardware for leak detection. Additionally, vehicle gas mileage may be increased since, in this approach, leak testing may be performed without using the engine. Further, accuracy of a leak test may be increased since such an approach does not depend on pressure and temperature correlations, for example. Further still, shorter test times may be employed in this approach which may result in a greater amount of flexibility in deciding when a leak test may be implemented.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.